The bondservant (o doulo) ... the son (o uio). There is a change in the metaphor by this contrast between the positions of the son and the slave in the house. The slave has no footing or tenure and may be cast out at any moment while the son is the heir and has a permanent place. Cf. Ishmael and Isaac ( Genesis 21:10 ) and Paul's use of it in Galatians 4:30 . We do not know that there is any reference here to Hagar and Ishmael. See also Hebrews 3:5 ( Numbers 12:7 ) for a like contrast between Moses as servant (qerapwn) in God's house and Christ as Son (uio) over God's house.